There has been an increasing use of sanitary absorbent articles including diapers each year. Currently, all the used sanitary absorbent articles are incinerated or disposed in a landfill. However, incinerating or disposing the articles in a landfill results in problems of lack of landfill sites or problems in that incineration results in high processing cost and adversely affects the environment due to carbon dioxide produced during the process, since used sanitary absorbent articles contain moisture comprising human waste such as urine.
Further, since large quantities of materials (resources) are consumed for manufacturing sanitary absorbent articles relative to the purpose of treating human waste, there has been an increasing demand for recycling or reusing sanitary absorbent articles. Thus, there is a need for efficient and economical processes for recycling used sanitary absorbent articles into individual constituents by decomposing or isolating main constituents of the absorbent articles without harming the environment.
A technique is desirable that is capable of isolating the constituents of sanitary absorbent articles into individual resources before used sanitary absorbent articles, such as diapers, can be recycled. In general, sanitary absorbent articles, such as baby diapers, consist of polypropylene (PP), polyethylene (PE), superabsorbent polymer (SAP), cellulose pulp, and the like.
Among the main components of sanitary absorbent articles, those such as polypropylene or polyethylene which are physically bound can be easily isolated by crushing, but the absorbent prepared by mechanically mixing superabsorbent polymers and cellulose pulp in a uniform distribution having a certain arrangement cannot be isolated into individual materials mechanically or by other physical measures, because superabsorbent polymers become a gel state as they absorb moisture from human waste to be swollen (i.e., become larger in volume) and are tangled with cellulose pulp fibers.
In order to isolate such superabsorbent polymers in a gel state and cellulose pulp into individual resources, superabsorbent polymers must be converted from a gel state to the original particle state by removing moisture absorbed by superabsorbent polymers.
Thus, in order to recycle used sanitary absorbent articles having an absorbent consisting of superabsorbent polymers and cellulose pulp by isolating their constituents into individual materials, a technique should be developed that makes it easier to isolate superabsorbent polymers and cellulose pulp into individual materials by allowing moisture absorbed by superabsorbent polymers to be discharged to convert the polymers from a gel state to the original particle state.
Korea Patent Laid-Open No. 2011-0029724 discloses separating superabsorbent polymers from a pulp by using chemicals such as bittern, acetic acid and hypochlorous acid, in order to isolate constituents of the absorbent wherein water is absorbed into individual materials. However, this technique has problems in that the substances used have a very irritating odor, generate harmful gases and are not easy to handle during the separating process. Another problem is the high cost of using bittern, for which additional purification or processing is required.
Further, techniques of recycling used diapers or the like by mechanically crushing and re-extruding into low grade fuels have been known, but such techniques are uneconomical and thus are impractical.